Oxfam has been using yammer for about 12 months now. As Mike said above, take-up has been strictly voluntary and word of mouth, but its now at the point where much of senior management are engaged with yammer on a daily or at least weekly basis and modeling its use. It's still early-mainstream: there are about 400 users and 3000 posts to date. We are using only the free version; at $3/user/month minimum for the paid version I doubt there would be a compelling business case.

In a global organisation spread across 50+ countries, I think its becoming useful to break down some geographic and hierarchical gaps. Its been very helpful for facilitating ambient awareness across the organisation, when emergencies have struck (eg recently in the Philippines). I think its the kind of tool that benefits from soft introduction - yes, give some parameters, and general guidance on how the tool *might* be useful, but let staff discover their own level and utility for it from the bottom up. If you have any other systems rollouts going on at the same time, some people may feel overwhelmed. I've found it useful to reassure colleagues that its in their control who they see/follow, and they can engage in it for 5 minutes a day and still see some benefit.

A possible con -- of the free version at least -- is that only staff on a single common domain (eg email addresses ending in @oxfam.org.uk) can participate. If you have other staff on a slightly different domain (eg @oxfam.org.sg) they cannot.

At FAO, we have just been approached by Yammer to become paid subscribers. At this moment, it does not seem to be a good option as the cost of $3 or $5 / month (based on the option selected) where most of our users have logged in only once. I think there is some potential for this tool if 1) it integrates well with the work (teams, distributed teams, existing communities) and 2) if they see a potential in it when compared to the Outlook mailbox.

We have just about 90 staff registered (we are approximately 4000). It all started bottom-up so there was no active promotion of the tool. We do not have any guidelines at this moment but might provide some basic social media Dos and Donts.

The usage so far shows that we have the usual suspects (Web 2.0 savvy) contributing bulk of the materials. The uses so far are:
1. Sharing internal information/links/resources and promoting initiatives (we use it disseminate things related to KM/KS)
2. Sharing interesting external links (normally through twitter)
3. Requests for information/help from colleagues
4. We have four groups but most of them are now inactive.
5. We tweeted/yammed live from the recent World Summit on Food Security.

Thanks Gauri, very helpful..
Yes, I wondered how long it would take before they start knocking at the door for a payment service. If it takes off, $3/$5 a month can soon mount up to a huge monthly bill.

We had a small trial amongst a set of random users in our firm a few months ago but decided not to go for it as we're probably a bit too small and our workforce too diverse.

The system is good and I think for a larger organisation, it's probably better. I understand that BT is trialling it, but you'll need to confirm that. Here are some of our thoughts and what some of our users experienced:

- a bit of confusion with the conversation threads (the desktop app view with the msn-style panel on the right) had one user responding to a message that followed hers, thinking it was a response although it was a separate thread.
- privacy was a potential issue for us with some silly user errors as people initially didn't realise it was transparent - so training is essential for users who are not accustomed to these technologies..
- encouraging usage: I found that setting up a few relevant discussion groups and inviting people, got them more interested

From an IT perspective, using Yammer via the website is probably better than using the desktop application - depends on your particular context though.

A monthly report from our IT dept ranked Yammer in the top 3 of network-based activity for our entire office. This is because the desktop app constantly checks back and forth for updates regardless of whether you're actually using it or not... this was despite the fact that only a handful of us had it installed.

I hope this helps a bit - we are much smaller though and every organisation is different!